Athletes at all levels of competition and fitness seek to test themselves and measure their abilities against both themselves and fellow competitors, e.g., as a gauge of one's fitness or improved progress. It would be useful to provide small and portable electronic devices that athletes could use for one or more purposes, for example: to provide performance measuring and feedback; to store collected data for display and/or later analysis; and to provide information and/or entertainment to the user. Further, it would be advantageous to provide easy, convenient, and lightweight activation and/or authentication systems for such electronic devices, e.g., to preserve battery life, to prevent measurement of data associated with undesired activity, and/or to prevent unauthorized use.